The present invention relates to optical fiber communication systems, and more particularly to a method and apparatus for sharing an optical source among a plurality of external optical modulators provided in different communication paths.
Optical fiber communication systems are well known. Such systems are enjoying increasing use in the telecommunications industry, in the cable television industry, and in local area networks used to couple personal computers and/or workstations together.
In the cable television industry, signal distribution via coaxial cable has dominated to date. Such systems are typically arranged in tree and branch networks that carry television program signals from a headend to various nodes that ultimately feed the cable signals to individual subscriber homes. Typically, the headend provides a single optical carrier signal that is modulated by RF subcarriers containing a plurality (e.g., 40-80) different television program channels. The carrier is communicated via the distribution path to individual subscriber homes, each of which receive the same television channel signals.
In certain situations, such as narrowcasting, it is desired to provide different programming to different subscribers. In narrowcasting, programming is directed to smaller audiences with special tastes, such as those who want foreign movies, folk music, performing arts, and the like. Although the provision of narrowcasting services can result in additional pay subscriptions for a cable system operator, in the past the incremental costs to the operator for implementing a narrowcasting system have tended to outweigh the incremental gains.
In an optical fiber distribution system, the provision of narrowcasting services has required separate signal lasers to generate a separate carrier for each band of narrowcast program channels that is to be added to the core channels offered to all subscribers. The need to provide a separate optical source for each category of narrowcast channels increases the cost and complexity of the distribution system. This has hampered the implementation of narrowcasting in emerging optical fiber distribution systems.
It would be advantageous to provide an optical fiber communication system that enables narrowcasting and other specialized programming schemes to be achieved at a relatively low cost with high system reliability. It would be further advantageous to provide such a system that utilizes known optical components and provides a high degree of flexibility in establishing, maintaining and revising the signal distribution plant. The present invention provides a method and apparatus for sharing an optical source among a plurality of different external optical modulators, thereby achieving the aforementioned advantages.